Transcript Bio 226: Cell and Molecular Biology

Water uptake
Path starts at root hairs
• Must take water from soil
• Ease depends on availability & how tightly it is bound
• Binding depends on particle size & chem
Water uptake
Availability depends on amount in soil pores
• Saturation: completely full
• Field capacity: amount left after gravity has drained
excess
• Permanent wilting point: amount where soil water
potential is too negative for plants to take it up
Plant Stress
1. Water?
2. Nutrients?
3. Environment?
• Temp?
• Pollution?
• Ozone, other gases?
• Herbicides, eg Round-Up, Atrazine?
• Insects and other herbivores?
• Pathogens = bacteria, viruses, fungi
• Salinity
Plant Stress
Next assignment: presenting a plant stressor, what is
known about it, and why it might affect plant 2˚
compounds in an ~ 10 minute presentation?
Alternative: presenting another good plant/stressor
response to study and why we should choose it over the
ones already presented.
Mineral Nutrition
Nutrients in soil
•Plants alter pH @ roots to aid uptake
• Also use symbionts
• Mycorrhizal fungi help: especially with P
• Some plants form symbioses with N-fixing prok.
Nutrient uptake
Most nutrients are dissolved in water
• Enter root through apoplast until hit endodermis
• Then must cross plasma membrane
Nutrient uptake
Then must cross plasma membrane
• Gases, small uncharged & non-polar molecules diffuse
down their ∆ [ ]
• Important for CO2, auxin & NH3 transport
Selective Transport
1) Channels
integral membrane proteins with pore that specific ions
diffuse through
Selective Transport
1) Channels
2) Facilitated Diffusion (carriers)
Carrier binds molecule
4 classes of Active transport ATPase proteins
1) P-type ATPases (P = “phosphorylation”)
2) V-type ATPases (V = “vacuole”)
3) F-type ATPases (F = “factor”)
4) ABC ATPases (ABC = “ATP Binding Cassette”)
• multidrug resistance proteins
Secondary active transport
Uses ∆ [ ] created by active transport to pump something
else across a membrane against its ∆ [ ]
Nutrient uptake
Gases enter/exit by diffusion down their ∆ [ ]
Ions vary dramatically!
Nutrient uptake
Gases enter/exit by diffusion down their ∆ [ ]
Ions vary dramatically!
H+ is actively pumped out of cell by P-type H+ -ATPase
Nutrient uptake
Ions vary dramatically!
H+ is actively pumped out of cell by P-type H+ -ATPase
and into vacuole by V-type ATPase & PPase
Nutrient uptake
H+ is actively pumped out of cell by P-type H+ -ATPase
and into vacuole by V-type ATPase & PPase
• Main way plants make membrane potential (∆Em)!
Nutrient uptake
H+ is actively pumped out of cell by P-type H+ -ATPase
and into vacuole by V-type ATPase & PPase
• Main way plants make membrane potential (∆Em)!
• Used for many kinds of transport!
Nutrient uptake
Many ions are imported by multiple transporters with
varying affinities
Nutrient uptake
Many ions are imported by multiple transporters with
varying affinities
• K+ diffuses through channels down ∆Em: low affinity
Nutrient uptake
Many ions are imported by multiple transporters with
varying affinities
• K+ diffuses through channels down ∆Em: low affinity
• Also taken up by H+ symporters : high affinity
Nutrient uptake
Many ions are imported by multiple transporters with
varying affinities
• K+ diffuses through channels down ∆Em: low affinity
• Also taken up by H+ symporters : high affinity
• Low affinity is cheaper
but less effective
Nutrient uptake
K+ diffuses through channels down ∆Em: low affinity
Also taken up by H+ symporters : high affinity
Low affinity is cheaper but less effective
some channels also transport Na+
Nutrient uptake
K+ diffuses through channels down ∆Em: low affinity
Also taken up by H+ symporters : high affinity
Low affinity is cheaper but less effective
some channels also transport Na+
why Na+ slows K+ uptake?
Nutrient uptake
K+ diffuses through channels down ∆Em: low affinity
Also taken up by H+ symporters : high affinity
Low affinity is cheaper but less effective
some channels also transport Na+
why Na+ slows K+ uptake?
Na+ is also expelled
by H+ antiport
Nutrient uptake
Na+ is also expelled
by H+ antiport
•Enters through channels
Ca2+ is expelled by P-type
ATPases in PM
Nutrient uptake
Ca2+ is expelled by P-type ATPases in PM
& pumped into vacuole & ER by H+ antiport & P-type
Nutrient uptake
Ca2+ is expelled by P-type ATPases in PM
pumped into vacuole & ER by H+ antiport & P-type
• enters cytosol via gated channels
Nutrient uptake
PO43-, SO42-, Cl- & NO3enter by H+ symport
Nutrient uptake
PO43-, SO42-, Cl- & NO3- enter by H+ symport
• also have anion transporters of ABC type
Nutrient uptake
PO43-, SO42-, Cl- & NO3- enter by H+ symport
• also have anion transporters of ABC type
• and anion channels
Nutrient uptake
PO43-, SO42-, Cl- & NO3- enter by H+ symport
• also have anion transporters of ABC type
• and anion channels
Plants take up N many ways
Nutrient uptake
Plants take up N many ways: NO3- & NH4+ are main
forms
Nutrient uptake
Plants take up N many other ways
• NO3- also by channels
• NH3 by diffusion
• NH4+ by carriers
Nutrient uptake
Plants take up N many other ways
• NO3- by channels
• NH3 by diffusion
• NH4+ by carriers
• NH4+ by channels
Nutrient uptake
Plants take up N many other ways
• 3 families of H+ symporters take up amino acids
Nutrient uptake
Plants take up N many other ways
•3 families of H+ symporters take up amino acids
•Also have many peptide transporters
• some take up di- & tripeptides by H+ symport
Nutrient uptake
Plants take up N many other ways
•3 families of H+ symporters take up amino acids
•Also have many peptide transporters
• some take up di- & tripeptides by H+ symport
• others take up tetra- &
penta-peptides by H+ symport
Nutrient uptake
Plants take up N many other ways
•3 families of H+ symporters take up amino acids
•Also have many peptide transporters
• some take up di- & tripeptides by H+ symport
• others take up tetra- &
penta-peptides by H+ symport
Also have ABC transporters
that import peptides
Nutrient uptake
Plants take up N many other ways
•3 families of H+ symporters take up amino acids
•Also have many peptide transporters
• some take up di- & tripeptides by H+ symport
• others take up tetra- &
penta-peptides by H+ symport
Also have ABC transporters
that import peptides
N is vital!
NO3- & NH4+ are main forms
Nutrient uptake
Metals are taken up by ZIP proteins & by ABC
transporters
• same protein may import Fe, Zn & Mn!
Nutrient uptake
Much is coupled to
pH gradient
Nutrient transport in roots
Move from soil to endodermis in apoplast
Nutrient transport in roots
Move from soil to endodermis in apoplast
Move from endodermis to xylem in symplast
Nutrient transport in roots
Move from endodermis to xylem in symplast
Transported into xylem by H+ antiporters
Nutrient transport in roots
Move from endodermis to xylem in symplast
Transported into xylem by H+ antiporters, channels
Nutrient transport in roots
Transported into xylem by H+ antiporters, channels,pumps
Nutrient transport in roots
Transported into xylem by H+ antiporters, channels,pumps
Lowers xylem water
potential -> root pressure
Water Transport
Passes water & nutrients to xylem
Ys of xylem makes root pressure
Causes guttation: pumping water into shoot
Transport to shoot
Nutrients move up
plant in xylem sap
Nutrient transport in leaves
Xylem sap moves through apoplast
Leaf cells take up what
they want
Nutrient assimilation
Assimilating N and S is
very expensive!
• Reducing NO3- to NH4+
costs 8 e- (1 NADPH +
6 Fd)
Nutrient assimilation
Assimilating N and S is
very expensive!
• Reducing NO3- to NH4+
costs 8 e- (1 NADPH +
6 Fd)
• Assimilating NH4+ into
amino acids also costs
ATP + e-
Nutrient assimilation
Assimilating N and S is very expensive!
• Reducing NO3- to NH4+ costs 8 e- (1 NADPH + 6 Fd)
• Assimilating NH4+ into amino acids also costs ATP + e• Nitrogen fixation costs 16 ATP + 8 e-
Nutrient assimilation
Assimilating N and S is very expensive!
• Reducing NO3- to NH4+ costs 8 e- (1 NADPH + 6 Fd)
• Assimilating NH4+ into amino acids also costs ATP + e• Nitrogen fixation costs 16 ATP + 8 e• SO42- reduction to S2- costs 8 e- + 2ATP
Nutrient assimilation
Assimilating N and S is very expensive!
• Reducing NO3- to NH4+ costs 8 e- (1 NADPH + 6 Fd)
• Assimilating NH4+ into amino acids also costs ATP + e• Nitrogen fixation costs 16 ATP + 8 e• SO42- reduction to S2- costs 8 e- + 2ATP
• S2- assimilation into Cysteine costs 2 more e• Most explosives are based on N or S!
Nutrient assimilation
Most explosives are based on N or S!
Most nutrient assimilation occurs in source leaves!
N cycle
Must convert N2 to a form that can be assimilated
• N2 -> NO3- occurs in atmosphere: lightning (8%) &
Photochemistry (2%) of annual total fixed
• Remaining 90% comes from biological fixation to NH4+
N cycle
Soil bacteria denitrify NO3- & NH4+ back to N2
• Plants must act fast!
• Take up NO3- & NH4+ but generally prefer NO3• Main form available due to bacteria
N assimilation by non-N fixers
Nitrate reductase in cytoplasm reduces
NO3- to NO2NO3- + NADPH = NO2- + NADP+
large enzyme with FAD & Mo cofactors
NO2- is imported to plastids & reduced
to NH4+ by nitrite reductase
N assimilation by non-N fixers
NO2- is imported to plastids & reduced
to NH4+ by nitrite reductase
NO2- + 6 Fdred + 8 H+ = NH4+ + 6 Fdox + 2 H2O
0.2% of NO2- is released as N2O : another reason rape &
corn biofuels increase global warming
N assimilation by non-N fixers
NO2- is imported to plastids & reduced
to NH4+ by nitrite reductase
NO2- + 6 Fdred + 8 H+ = NH4+ + 6 Fdox + 2 H2O
0.2% of NO2- is released as N2O : another reason rape &
corn biofuels increase global warming
Regulated at NO3- reductase; always << NO2- reductase
NO2- is toxic!
N assimilation by non-N fixers
Regulated at NO3- reductase; always << NO2- reductase
NO2- is toxic!
NR induced by light & nitrate
N assimilation by non-N fixers
Regulated at NO3- reductase; always << NO2- reductase
NO2- is toxic!
NR induced by light & nitrate
Regulated by kinase in dark, dephosphorylation in day
NH4 assimilation
GS -> GOGAT
1. Glutamate + NH4+ + ATP <=> Glutamine + ADP +Pi
GS -> GOGAT
1. Glutamate + NH4+ + ATP <=> Glutamine + ADP +Pi
2. Glutamine + a-ketoglutarate + NADH/2 Fdred <=>
2 Glutamate + NAD+/ 2 Fdox
GS -> GOGAT
1. Glutamate + NH4+ + ATP <=> Glutamine + ADP +Pi
2. Glutamine + a-ketoglutarate + NADH/2 Fdred <=>
2 Glutamate + NAD+/ 2 Fdox
3. Fd GOGAT lives in source cp
GS -> GOGAT
Fd GOGAT lives in source cp
• NADH GOGAT lives in sinks
GS -> GOGAT
1. Glutamate + NH4+ + ATP <=> Glutamine + ADP +Pi
2. Glutamine + a-ketoglutarate + NADH/2 Fdred <=>
2 Glutamate + NAD+/ 2 Fdox
3. Use glutamate to make other a.a. by transamination
GS -> GOGAT
3. Use glutamate to make other a.a. by transamination
Glutamate, aspartate & alanine can be converted to the
other a.a.
S assimilation
SO42- comes from weathering or from rain: now an
important source! Main thing that makes rain acid!
S assimilation
S is used in cysteine & methionine
S assimilation
S is used in cysteine & methionine
Also used in CoA, S-adenosylmethionine
S assimilation
S is used in cysteine & methionine
Also used in CoA, S-adenosylmethionine
Also used in sulphoquinovosyl-diacylglycerol
S assimilation
S is used in cysteine & methionine
Also used in CoA, S-adenosylmethionine
Also used in sulphoquinovosyl-diacylglycerol
And in many storage compounds: eg allicin (garlic)
S assimilation
SO42- comes from weathering or from rain: now an
important source! Main thing that makes rain acid!
Some bacteria use SO42- as e- acceptor -> H2S
S assimilation
SO42- comes from weathering or from rain: now an
important source! Main thing that makes rain acid!
Some bacteria use SO42- as e- acceptor -> H2S
Some photosynthetic bacteria use reduced S as e- donor!
S assimilation
SO42- comes from weathering or from rain: now an
important source! Main thing that makes rain acid!
Some bacteria use SO42- as e- acceptor -> H2S
Some photosynthetic bacteria use reduced S as e- donor!
Now that acid rain has declined in N. Europe Brassica &
wheat need S in many places
S assimilation
SO4 2- is taken up by roots &
transported to leaves in xylem
Most is reduced in cp
S assimilation
SO4 2- is taken up by roots &
transported to leaves in xylem
Most is reduced in cp
1. add SO4 2- to ATP -> APS
S assimilation
1. add SO4 2- to ATP -> APS
2. Transfer S to Glutathione -> S-sulfoglutathione
S assimilation
1. add SO4 2- to ATP -> APS
2. Transfer S to Glutathione -> S-sulfoglutathione
3. S-sulfoglutathione + GSH -> SO32- + GSSG
1.
2.
3.
4.
S assimilation
add SO4 2- to ATP -> APS
Transfer S to Glutathione -> S-sulfoglutathione
S-sulfoglutathione + GSH -> SO32- + GSSG
Sulfite + 6 Fd -> Sulfide
1.
2.
3.
4.
5.
•
S assimilation
add SO4 2- to ATP -> APS
Transfer S to Glutathione -> S-sulfoglutathione
S-sulfoglutathione + GSH -> SO32- + GSSG
Sulfite + 6 Fd -> Sulfide
Sulfide + O-acetylserine -> cysteine + acetate
O-acetylserine was made from serine + acetyl-CoA
S assimilation
Most cysteine is converted to
glutathione or methionine
S assimilation
Most cysteine is converted to
glutathione or methionine
Glutathione is main form
exported
S assimilation
Most cysteine is converted to
glutathione or methionine
Glutathione is main form
exported
Also used to make many other
S-compounds
S assimilation
Most cysteine is converted to
glutathione or methionine
Glutathione is main form
exported
Also used to make many other
S-compounds
Methionine also has many uses
besides protein synthesis
S assimilation
Most cysteine is converted to glutathione or methionine
1. Cys + homoserine -> cystathione
S assimilation
Most cysteine is converted to glutathione or methionine
1. Cys + homoserine -> cystathione
2. Cystathione -> homocysteine + Pyruvate + NH4+
S assimilation
Most cysteine is converted to glutathione or methionine
1. Cys + homoserine -> cystathione
2. Cystathione -> homocysteine + Pyruvate + NH4+
3. Homocysteine + CH2=THF -> Met + THF
4. 80% of met is converted to S-adenosylmethionine &
used for biosyntheses
S assimilation
Most cysteine is converted to glutathione or methionine
Glutathione is made enzymatically!
1. Glutamate + Cysteine -> g-glutamyl cysteine
S assimilation
Glutathione (GluCysGly) is made enzymatically!
1. Glutamate + Cysteine -> g-glutamyl cysteine
2. g-glutamyl cysteine + glycine -> glutathionine
S assimilation
Glutathione (GluCysGly) is made enzymatically!
1. Glutamate + Cysteine -> g-glutamyl cysteine
2. g-glutamyl cysteine + glycine -> glutathionine
Glutathione is precursor for many chemicals, eg
phytochelatins
S assimilation
Glutathione (GluCysGly) is made enzymatically!
1. Glutamate + Cysteine -> g-glutamyl cysteine
2. g-glutamyl cysteine + glycine -> glutathionine
Glutathione is precursor for many chemicals, eg
phytochelatins
SAM & glutathione are also precursors for many cell wall
components
Assignment 1
Pick a secondary compound and figure out how to
measure it
Assignment 2
Design a way to see how plants are responding to the
stress